Elucidating the Fragmentation Pathways of Cyclic and Linear Poly(dimethylpropanoate) via Tandem Mass Spectrometry and Ion Mobility Mass Spectrometry

More than one-half of the world’s plastic waste comes from poorly recyclable polymers, such as polyethylene and polypropylene. The increased accumulation of plastic waste is a growing environmental challenge. This led to the employment of polyesters with controlled degradation behavior for a variety of materials applications. Understanding the relationship between polymer structure and fragmentation pathways is essential for designing materials that balance durability and sustainability. Polyesters and polyamides with an Cα adjacent to the carbonyl, fragment via 1,5- and 1,3-hydrogen rearrangements; however, the fragmentation of a polyester where an is not present adjacent to the carbonyl has not been researched thoroughly. This work reports the first detailed characterization of the fragmentation behavior of both linear and cyclic poly(dimethylpropanoate) (poly(DMP)). Poly(DMP) possesses a neopentyl carbon which slows degradation and inhibits the typical 1,5-hydrogen rearrangements common in other polyesters. Cyclic poly(DMP) undergoes ring opening at various points before fragment generation, resulting in a mixture of ring-opened linear species, while the linear polymer predominantly fragments through single-bond cleavages. Additionally, the fragmentation patterns are influenced by poly(DMP) end groups, with distinct patterns observed for hydroxyl-terminated, halogen-terminated, and pyridinium-initiated polymers. Moreover, ion mobility mass spectrometry (IM-MS) effectively distinguishes isomeric fragments in cyclic poly(DMP) based on the differences in the collision cross-section of cyclic precursor and the resulting linear fragment ions.